12 The Ankle and Foot: Diagnostic Imaging

10.1055/b-0038-161017

12 The Ankle and Foot: Diagnostic Imaging

Abstract

Given the superficial location of many structures around the ankle and foot, ultrasound examination together with plain X-rays may now be considered to be the “first-line” technique for imaging many patients with ankle and foot pathologies. Recent advances in ultrasound technology, including developments of high-resolution probes and enhanced software capabilities, have led to an improvement in image quality. In addition, ultrasound is particularly useful in allowing dynamic assessment of structure including ligament patency.

Due to the superficial position of most ankle and foot structures ultrasound examination should be undertaken with a high frequency probe of (12–18 MHz). A large foot-print linear probe gives better anatomical resolution; however, a smaller footprint “hockey stick” probe should also be available for smaller structures and for interventional work.

12.1 Diagnostic Imaging of the Ankle and Foot: Introduction

The ankle may be considered as consisting of four quadrants, anterior, medial, lateral, and posterior with the foot being considered separately. Ultrasound would normally be focused only one or two of these quadrants or the foot depending on the clinical diagnosis.

Imaging of the ankle and foot includes the following:

Anterior
- Tibialis anterior muscle and tendon.
- Extensor hallucis longus muscle and tendon.
- Extensor digitorum longus muscle and tendon.
- Deep peroneal nerve and dorsalis pedis artery.
- Talocrural joint including anterior joint recess.
- Anterior tibiofibular ligament.
- Talonavicular joint.
- Navicular-cuneiform and intercuneiform joints.
- Tarsometatarsal joints.
Medial
- Posterior tibialis muscle and tendon.
- Flexor digitorum longus muscle and tendon.
- Flexor hallucis longus muscle and tendon.
- Posterior tibial nerve and medial and lateral plantar nerves.
- Tibial artery and veins.
Lateral
- Peroneus longus and brevis muscle and tendon.
- Anterior talofibular ligament (including dynamic stressing—the sonographic draw test—as indicated).
- Calcaneofibular ligament.
- Calcaneocuboid joint.
Posterior
- Achilles tendon and insertion.
- Posterior calcaneum.
- Gastrocnemius and soleus muscles and musculotendinous junctions.
- Plantaris tendon (may be absent).
- Retrocalcaneal bursa.
- Kager’s fat and posterior aspect of tibiotalar joint (os trigonum if present).
Inferior
- Plantar fascia origin at anteromedial calcaneal tubercle (including dynamic stressing).
Interdigital
- Dynamic scanning for a Morton’s neuroma if present (ultrasonographic Mulder’s click test).
- Intermetatarsal bursa (if present).
Digital
- Assess for synovitis, dorsal, and/or plantar.
- Dorsal aspect of the metatarsophalangeal joints including metatarsal recess.
- Plantar aspect of metatarsophalangeal joints including plantar plate.
- First metatarsophalangeal joint including sesamoid bones.
- Interphalangeal joints as indicated.

12.1.1 Anterior

Anterior Ankle Joint: Longitudinal Scan

Fig. 12.1 Longitudinal scan of the anterior aspect of the ankle joint. The probe is placed in the anatomical sagittal plane over the talocrural joint. The foot is in a plantar flexed position to allow better visualization of the talar dome and facilitate a good contact of the probe with the ankle. The probe should be moved from medial to lateral to fully examine the whole joint.

Fig. 12.2 Longitudinal image of the anterior aspect of the talocrural joint and talus. The image demonstrates the anterior edge of the tibia (Tib), the talar dome (TD) and articular cartilage (*white arrows*), the head of the talus (HT), and the anterior talar recess (*white star*). The anterior talocrural capsule can be seen to extend over the talar dome and anterior recess (*yellow arrows*).

Fig. 12.3 Sagittal view of the medial aspect of the right ankle and foot. The sustentaculum tali may be seen immediately below the body of the talus. It is a horizontal shelf that arises from the anteromedial portion of the calcaneus. The superior surface is concave and articulates with the middle calcaneal surface of the talus. The inferior surface has a groove for the tendon of flexor hallucis longus. The navicular tuberosity forms a rounded eminence on the medial surface of the navicular bone anterior to the talus giving attachment to a part of the tendon of the tibialis posterior muscle. An accessory bone known as an os naviculare accessorium (also known as an os tibiale externum) is a large accessory ossicle that can be present adjacent to the medial side of the navicular tuberosity. The tibialis posterior tendon often inserts with a broad attachment into the ossicle. An os naviculare is present in approximately 10% of the population and more common in female patients. The medial cuneiform (also known as first cuneiform) is the largest of the cuneiforms situated anterior to the navicular bone and posterior to the base of the first metatarsal. The tibialis anterior and peroneus longus tendon inserts onto the medial cuneiform bone. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Anterior Ankle Joint: Transverse Scan

The patient is positioned in supine with the knee flexed to approximately 90 degrees flexion and the foot placed on the couch so that it lies in a plantar flexed position. This facilitates a better visualization of the talar dome. The probe is placed in the anatomical transverse plane so that it lies over the anterior aspect of the talar dome (Fig. 12‑4 , Fig. 12‑5 , Fig. 12‑6 ).

Fig. 12.4 Transverse scan of the anterior aspect of the ankle joint. The probe is placed in the anatomical transverse plane over the talocrural joint and the talar dome. The probe should be moved from proximal to distal to fully assess the lower tibia, talocrural joint, and the talar dome in turn.

Fig. 12.5 Transverse image of the ankle at the level of the talar dome (TD). The most medial tendon is that of tibialis anterior which can be seen to advance in a medial direction toward its insertion onto the medial cuneiform and base of the first metatarsal. The next tendon is that of extensor hallucis longus (EHL). The most laterally placed tendon is that of extensor digitorum longus (EDL) which if followed distally may be seen to split into four slips to insert into dorsal aponeuroses and the bases of the distal phalanges of the second through fifth toes. Lying between and deep to the tendons of EHL and EDL is found the anterior tibial artery (A) and the deep peroneal nerve (*yellow circle*). TA, tibialis anterior tendon; white arrows, articular cartilage over the talar dome.

Fig. 12.6 Coronal view of the anterior aspect of the ankle and foot demonstrating the tendon sheaths and retinacula. From medial to lateral the order of tendons is tibialis anterior, flexor hallucis longus, and flexor digitorum longus. The superior extensor retinaculum binds down the tendons of extensor digitorum longus, extensor hallucis longus, fibularis tertius (also known as peroneus tertius), and tibialis anterior as they descend on the front of the tibia and fibula. Under it are also found the anterior tibial vessels and deep peroneal nerve. The inferior extensor retinaculum is a Y-shaped structure placed in front of the ankle joint. The stem of the Y is attached laterally to the upper surface of the calcaneum anterior to interosseous talocalcaneal ligament. It is directed medially as a double layer with one lamina passing in front of and the other behind the tendons of the peroneus tertius and extensor digitorum longus. At the medial border of the tendon of extensor digitorum longus the two layers join together forming a compartment in which the tendons are enclosed. From the medial edge of the extensor digitorum longus tendon the two limbs of the Y diverge. One is directed proximally and medially to be attached to the medial malleolus, passing over the extensor hallucis longus but enclosing the tibialis anterior by splitting of its fibers. The second limb of the Y extends distally and medially to be attached to the border of the plantar aponeurosis passing over the tendons of the extensor hallucis longus and tibialis anterior. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Anterior Midfoot: Longitudinal Scan

The patient is positioned in supine with the knee flexed to approximately 90 degrees of flexion and the foot placed on the couch so that it lies in a plantar flexed position. This facilitates a better visualization of the midfoot region and fixes the foot in a stable position. The probe is initially placed in the anatomical sagittal plane so that it lies over the dorsum of talonavicular and navicular cuneiform joints. Moving the probe from medial to lateral allows visualization of the medial, middle, and lateral cuneiform bones and their articulation with the navicular. If the probe is moved distally, the tarsometatarsal joints may be seen (Fig. 12‑7 , Fig. 12‑8 , Fig. 12‑9 ).

Fig. 12.7 Longitudinal image of the medial aspect of the midfoot. The talar dome may be seen to the left of the image. The head of the talus (HT) articulates with the navicular (NAV) at the talonavicular joint (*yellow arrowhead*). The navicular may be seen to articulate with the medial cuneiform (Medcun) to the right of the image (*white arrowhead*).

Fig. 12.8 Longitudinal image of the medial aspect of the midfoot. In this image the probe has been moved distally from the image outlined in Fig. 12‑7 . The navicular (NAV) may be seen to the left of the image. The white arrowhead indicates the navicular medial cuneiform joint. The medial cuneiform (Medcun) may be seen to articulate with the base of the first metatarsal (MT1) at the first tarsometatarsal joint (*curved yellow arrow*).

Fig. 12.9 Transverse view of the superior aspect of the bones of the right foot and ankle. The midfoot is composed of five of the seven tarsal bones, the navicular, cuboid, and the three cuneiform bones. These can be thought of as being arranged in two irregular rows with the cuboid occupying space in both rows. The proximal row contains the navicular (on the medial side of the foot) and the cuboid (on the lateral side). The distal row contains the three cuneiforms (medial, intermediate, and lateral) and the cuboid (lateral to the lateral cuneiform). The boundary between the midfoot and forefoot consists of the five tarsometatarsal joints. The medial, intermediate, and lateral cuneiforms articulate with the first, second, and third metatarsals, respectively. The cuboid articulates with the fourth and fifth metatarsals. In addition, there are also multiple joints within the midfoot itself. The distal row of the midfoot has two intercuneiform joints (between adjacent cuneiforms) and a cuneocuboid joint (between the lateral cuneiform and the cuboid). Proximally the three cuneiforms articulate with the navicular bone (the cuneonavicular joints). In some individuals, there is also a small articulation between the cuboid and navicular. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Anterior Ankle: Anterior Tibiofibular Ligament

The patient is positioned in supine with the foot over the edge of the couch. This allows the clinician to move the foot to stress the ligament and assess for patency. The probe is placed in the anatomical transverse oblique plane so that it lies longitudinally over the anterior aspect of the lateral malleolus and anterior distal tibia. The ligament may be assessed dynamically by maintaining the probe position while the patient’s foot is passively dorsiflexed placing stress through the ligament as the wider anterior talar dome enters the ankle mortise (Fig. 12‑10 , Fig. 12‑11 ).

Fig. 12.10 Longitudinal scan of the anterior tibiofibular ligament of the ankle. The probe is placed in the anatomical transverse oblique plane so that its lateral edge is over the anterior aspect of the lateral malleolus. The more medial edge of the probe is angled so that it is in a more superior position.

Fig. 12.11 Longitudinal image the anterior tibiofibular ligament of the ankle. The ligament (*yellow arrowheads*) may be seen as an echogenic band of fibrillar pattern extending from the lateral malleolus (LM) medially to the anterior aspect of the distal tibia. In this image the foot has been placed in dorsiflexion to place stress through the ligament which appears taught. Some fluid (*white star*) is noted deep to the ligament in this patient who had recently twisted the ankle LM, anterior aspect of the lateral malleolus; white star, fluid deep to ligament; yellow arrowhead, anterior tibiofibular ligament of the ankle.

Anterior Ankle Joint and Foot: Pathology

See Fig. 12‑12 , Fig. 12‑13 , Fig. 12‑14 a–c; Fig. 12‑15 a,b; Fig. 12‑16 a–c.

Fig. 12.12 Longitudinal image of the midfoot and the lateral cuneiform (LC) and third metatarsal (MT3) joint. The image demonstrates marked cortical irregularity of both the cuneiform and base of the third metatarsal in keeping with osteophytosis (*white arrowheads*). In addition, there appears to be some soft tissue hypertrophy of the joint (*curved arrow*). These findings are in keeping with marked osteoarthritic change of the joint.

Fig. 12.13 Longitudinal image of the midfoot and middle cuneiform (MC) and second metatarsal (MT2) joint. There is a significant degenerative change within the joint with an associated soft tissue hypertrophy (*curved arrow*) and osteophyte (*white arrowhead*).The image demonstrates a guided injection into the joint with the needle being advanced from distally to proximal from the right side (*yellow arrows*). Yellow arrows indicate the needle.

Fig. 12.14 **(a)** Longitudinal image of the tendon of tibialis anterior (TA) over the anterior aspect of the ankle joint. The tendon is of good fibrillar pattern and appears echogenic other than a longitudinal intrasubstance region (*curved arrow*) suggestive of a possible intrasubstance tear. There is, however, both an effusion (*white star*) and synovial thickening (*yellow arrows*) within the tendon sheath in keeping with a tenosynovitis. **(b)**Transverse image of the tendon of tibialis anterior (TA) demonstrated in part (a). The tendon in this image appears intact with no evidence of intrasubstance pathology. There is, however, significant effusion around the tendon (*white star*) and synovial thickening (*yellow arrow*s). In addition, in this image Power Doppler demonstrates an active synovitis in keeping with tenosynovitis. **(c)** Transverse image of the tendon of tibialis anterior (TA) as demonstrated in parts (a) and (b). In this image a needle has been introduced into the tendon sheath in short axis (*white arrow*) prior to injection of corticosteroid into the sheath. Curved arrow, loss of normal intrasubstance fibrillar pattern; white arrow, needle; white star, fluid within tendon sheath; yellow arrows, synovial thickening.

Fig. 12.15 (a) Longitudinal image of the tendon of tibialis anterior (TA) over the anteromedial aspect of the ankle. The tendon appears intact at this level; however, it has a “wavy-like” appearance despite the tendon being placed in a stretched position (*yellow arrows*). This is strongly suggestive of a rupture more distally (see part[b]). (b) Longitudinal image of the tendon of tibialis anterior (TA) over its distal portion close to its insertion onto the navicular tubercle and medial cuneiform. The image is of the same tendon as in part (a). There appears significant discontinuity within the tendon with retraction and bunching of the tendon proximally (*curved arrows*). In addition, there appears posterior enhancement behind the retracted tendon (*white arrowheads*) indicating a loss of tendon density. Distally there is a loss of normal tendon architecture (*white arrows*). The image is in keeping with a rupture of tibialis anterior toward its insertion.

Fig. 12.16 (a) Transverse image of the dorsal aspect of the midfoot region. The image demonstrates a lobulated anechoic swelling measuring approximately 4 cm transversely. Note the posterior enhancement (*yellow arrows*). These findings are typical of an arthrosynovial cyst/ganglion. (b) Transverse image of the dorsal aspect of the midfoot. The image is the same as demonstrated in part (a). A needle may be seen within the ganglion which is being aspirated (*curved arrow*). (c) Transverse image of the dorsal aspect of the midfoot. The image is the same as demonstrated in parts (a) and (b). The image shows the ganglion decreasing in size as aspiration continues (*curved arrow*). Curved arrow, needle being used to aspirate ganglion.

12.1.2 Medial

Medial Ankle Joint: Transverse Scan

The patient is positioned in supine with the leg placed in external rotation to allow visualization of the structures laying immediately posterior to the medial malleolus. The probe is placed in the transverse plane behind the malleolus. The anterior edge of the probe should lay on the malleolus with the posterior edge of the probe reaching toward the Achilles tendon. A small cushion placed under the ankle and foot may allow for an improved contact of the probe with the patient (Fig. 12‑17 , Fig. 12‑18 , Fig. 12‑19 ).

Fig. 12.17 Transverse image of the medial aspect of the ankle. The probe is positioned in the transverse plane behind the medial malleolus to view the structures within the tarsal tunnel.

Fig. 12.18 Transverse image of the tarsal tunnel posterior to the medial malleolus. The first tendon seen is that of tibialis posterior (TP). Immediately posterior to this is the tendon of flexor digitorum longus (FDL). More posterior and deeper lying between the posterior medial and lateral talar tubercles is the tendon of flexor hallucis longus (FHL). This arrangement of tibialis posterior, flexor digitorum longus, and flexor hallucis longus affords the mnemonic Tom, Dick, and Harry. Immediately above the tendon of flexor hallucis longus can be seen the tibial nerve prior to it splitting into the medial and lateral plantar nerves (*yellow oval*). Above this the tibial artery (*red circle*) may be seen accompanied by a vein on either side. Red circle, posterior tibial artery; yellow arrows, flexor retinaculum; yellow oval, tibial nerve.

Fig. 12.19 Sagittal view of the medial aspect of the right ankle illustrating the tendon sheaths and retinacula. The tarsal tunnel is the fibro-osseous canal found posterior and inferior to the medial malleolus. The roof of the tarsal tunnel is formed by the flexor retinaculum which extends from the medial malleolus posteriorly and obliquely downward to insert onto the medial aspect of the calcaneum. The floor of the tunnel is formed by the medial surfaces of both the talus and calcaneum. From anterior to posterior the contents of the tarsal tunnel are the tibialis posterior tendon, the flexor digitorum longus tendon, the neurovascular bundle consisting of the posterior tibial artery, vein, and tibial nerve, and most posteriorly situated between the posterior medial and lateral talar tubercles the tendon of flexor hallucis longus. The tibial nerve may be seen to split into the medial and lateral plantar nerves within the tarsal tunnel. A useful mnemonic to remember the order of structures in the tarsal tunnel is Tom, Dick, and A Very Nervous Harry. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Medial Ankle Joint: Longitudinal Scan

With the patient’s ankle and foot in the same position as for a transverse scan of the medial ankle the probe is turned through 90 degrees so that it lies in the transverse oblique plane to view the structures within the tarsal tunnel. With the probe more anteriorly placed, the tendon of tibialis posterior may be seen. As the probe is moved posteriorly over the tarsal tunnel, the tendon of flexor digitorum longus is next visualized followed by the tibial nerve, posterior tibial artery, and the deeply placed tendon of flexor hallucis longus (Fig. 12‑20 a,b).

Fig. 12.20 (a) Longitudinal image of the tibialis posterior tendon (TP) as it passes posteriorly and then inferiorly to the medial malleolus. The tendon becomes anisotropic as it curves around the malleolus (*curved arrow*). (b) Longitudinal image of the tarsal tunnel at the ankle. The probe has been placed more posteriorly over the tarsal tunnel allowing visualization of the posterior tibial artery (A), tibial nerve (N), and more deeply to these two structures the tendon of flexor hallucis longus (FHL) lying between the posterior medial and lateral talar tubercles.

Medial Foot Joint: Longitudinal Scan

Having viewed the tendon of tibialis posterior around the posterior aspect of the medial malleolus as it passes through the tarsal tunnel, the tendon may be followed distally to its insertion onto the tuberosity of the navicular and medial cuneiform (Fig. 12‑21 , Fig. 12‑22 a,b).